Histological definition of the vomeronasal organ in humans and chimpanzees, with a comparison to other primates

Abstract

The vomeronasal organ (VNO) is a chemosensory structure that has morphological indications of functionality in strepsirhine and New World primates examined to date. In these species, it is thought to mediate certain socio-sexual behaviors. The functionality and even existence of the VNO in Old World primates has been debated. Most modern texts state that the VNO is absent in Old World monkeys, apes, and humans. A recent study on the VNO in the chimpanzee (Smith et al., 2001b) challenged this notion, demonstrating the need for further comparative studies of primates. In particular, there is a need to establish how the human/chimpanzee VNO differs from that of other primates and even nonhomologous mucosal ducts. Histochemical and microscopic morphological characteristics of the VNO and nasopalatine duct (NPD) were examined in 51 peri- and postnatal primates, including humans, chimpanzees, five species of New World monkeys, and seven strepsirhine species. The nasal septum was removed from each primate and histologically processed for coronal sectioning. Selected anteroposterior intervals of the VNO were variously stained with alcian blue (AB)-periodic acid-Schiff (PAS), PAS only, Gomori trichrome, or hematoxylin-eosin procedures. All strepsirhine species had well developed VNOs, with a prominent neuroepithelium and vomeronasal cartilages that nearly surrounded the VNO. New World monkeys had variable amounts of neuroepithelia, whereas Pan troglodytes and Homo sapiens had no recognizable neuroepithelium or vomeronasal nerves (VNNs). Certain unidentified cell types of the human/chimpanzee VNO require further examination (immunohistochemical and electron microscopic). The VNOs of P. troglodytes, H. sapiens, and New World monkeys exhibited different histochemistry of mucins compared to strepsirhine species. The nasopalatine region showed great variation among species. It is a blind-ended pit in P. troglodytes, a glandular recess in H. sapiens, a mucous-producing duct in Otolemur crassicaudatus, and a stratified squamous passageway in all other species. This study also revealed remarkable morphological/histochemical variability in the VNO and nasopalatine regions among the primate species examined. The VNOs of humans and chimpanzees had some structural similarities to nonhomologous ciliated gland ducts seen in other primates. However, certain distinctions from the VNOs of other primates or nonhomologous epithelial structures characterize the human/chimpanzee VNO: 1) bilateral epithelial tubes; 2) a superiorly displaced position in the same plane as the paraseptal cartilages; 3) a homogeneous, pseudostratified columnar morphology with ciliated regions; and 4) mucous-producing structures in the epithelium itself.

The vomeronasal organ of greater bushbabies (Otolemur spp.): Species, sex, and age differences

“…As such, they provide the most appropriate model to understand primitive aspects of the accessory olfactory system in primates. In this regard, the present study supports existing notions that strepsirrhines have VNOs that resemble those of other mammals with functional VNOs Hunter et al, 1987;Loo & Kanagasuntheram, 1972;Smith et al, 2002).…”

“…Terminology for the vomeronasal organ varies. Herein, we follow the usage of Bhatnagar and Meisami (1998) and Smith et al (2001aSmith et al ( , 2002 which considers the VNO to comprise a neuroepithelial tube that, in many species, also includes a receptor-free zone.…”

New perspectives on anthropoid origins

“…The VNO is the primary receptor organ of the AOS, and accordingly much attention recently has been devoted to the presence or absence of this structure among primates. Catarrhines are unique among primates in lacking functional VNOs (91,96). Early reports of a functional VNO in humans are controversial and have not been supported by subsequent anatomical research (97,98).…”

Ontogeny of the nasopalatine duct in primates

“…Clearly, the timing of NPD patency differs among callitrichids, and further examinations of more taxa will reveal how much variation exists. At present, it is interesting to note that the species with later patency of the NPD (S. geoffroyi), appeared to have less sensory epithelium in the VNO at birth (Smith et al, 2002(Smith et al, , 2003unpublished data).…”

“…On the other hand, certain special senses, such as chemosensation, are well developed at birth (Schaal et al, 1998;Steiner et al, 2001). Furthermore, the VNOs of primates appear to vary in their morphological maturity at birth, with strepsirhines generally showing a better-developed neuroepithelium than haplorhines (Smith et al, 2002). Thus, primates provide an interesting test for the hypothesis that the maturation of the ducts leading to the VNO is related to the degree of infant dependency (Wöhrmann-Reppening and Barth-Mü ller, 1994).…”